Switches can be used upon a substrate such as a printed circuit board (PCB), or a similar rigid or flexible substrate which features appropriate conductive pads and tracks upon its surface. When combined with the conductive pads and connecting tracks of the substrate, the switch is able to operate as an electrical switch which may be connected to an associated electrical circuit. Such an associated circuit will generally be some type of system incorporating electronic logic functions. Such an associated circuit might be a device which incorporates discreet electronic logic components or a micro-controller to interpret and act in accordance with, the signals conveyed from a key-pad.
Such applications are presently served by devices commonly known as dome-switches, or simply as domes. These devices are made as a domed element, with a round or other derived shape from conductive sheet material, generally a very thin, resilient metal with spring properties which cause it to return to its formed shape when any actuating forces are released. High volumes of domes are widely used in electronics industries in conjunction with a range of various ancillary applied materials and systems, the essential purpose of which is to contain and retain the domed contact elements, stationed upon printed-circuit substrate materials.
In contemporary laminated key-panels, the shape of the domed element used serves two purposes:
First, the central portion of the domed element, in its relaxed or un-actuated state, is raised above the plane of the element's rim, ensuring that the central portion is poised above, yet electrically isolated from, a contact surface below the dome. This contact surface is generally provided on some type of printed circuit board which acts as a substrate upon which the dome is positioned to form an electrical switch. The clearance between these two elements is generally about one or two millimetres. The rim of the dome, when not actuated by a force which would distort its shape, is the only part of the unit which is in contact with an associated substrate, such as a PCB. Upon such a PCB is a conductive pad, generally in the form of a full or partial annular ring, upon which the dome's rim sits, being electrically in contact with it. This rim-contact pad is electrically isolated from a centralised contact pad which forms the second node of a simple switch, with the contacting element being the dome itself.
Second, the shape of the dome and the springy nature of the sheet material from which it is formed means that, when the dome's central portion is depressed (by a finger), it can be caused to deform in a sudden or “snap” action. The element, partly “flattened” in this way, can be made to electrically connect the inner and outer contact-pads upon a substrate such as a PCB. As this actuating pressure is steadily released, the domed element, due to the effects of its mechanical hysteresis will delay its return to its normal, un-actuated state, until it suddenly releases with a “snap-action”. This snap-action serves the very important function of providing tactile feedback to a human operator of the key-panel switch, ie; it signals to the operator the impression that a switching action has indeed occurred. This hysteresis also serves as a contact de-bounce mechanism, although this is not crucial these days because micro-controller programs, as commonly seen in situations using dome-switch key-pad fabrications, can easily ignore the effects of contact-bounce.
These dome can have problems of migration especially when used in a vertical position and the edges of the dome can wear away the conductive track on the PCB and so cause failure of the switching function.
It is an object of this invention to provide an alternative switch element suitable for surface mounting onto a PCB or to at least provide a useful alternative.